The primary goal is to support the subprojects by supplying precise and accurate biochemical measurements of markers of bone formation and bone resorption, calcium-regulating hormones, calcium absorption, sex steroids, and IGF and growth hormone. Bone formation will be assessed by serum osteocalcin and serum bone alkaline phosphatase. Bone resorption will be assessed by serum tartrate resistant acid phosphatase, urinary deoxypyridinoline and urinary n-telopeptide crosslinks. Calcium-regulating hormones will be assessed by serum parathyroid hormone, serum 250H vitamin D, and serum 1,25(OH)2 vitamin D. Calcium absorption will be assessed from the specific activity in serum following an oral dose of stable calcium labeled with radiocalcium. The sex steroids will be assessed by serum estradiol, estrone sulphate, estrone, testosterone, androstenedione, dehydroepiandrosterone and dehydroepiandrosterone sulphate, and sex- hormone binding globulin. Growth hormone will be assessed by measurements of urinary growth hormone and serum IGF and IGF-BP3. The biochemistry core will also be responsible for ensuring that all biological samples are logged-in, processed and stored under optimal conditions; that assays are performed with precision and accuracy; that the data generated are entered in the biochemistry database and transferred in a timely fashion to the biostatistical core for merging with clinical variables for analysis.